Desert aerosols

Individual dust storms from the Sahara desert have been shown to transfer material from the northwest coast of Africa, across the Atlantic, to the east coast of the United States (Ott et al. 1991). For example, Prospero et al. (1987) suggested that enough Saharan dust is carried into the Miami area to significantly reduce visibility during the summer months. Similar dust transport occurs from the deserts of Asia across the Pacific Ocean 

FIGURE 8.22 Typical desert aerosol number, surface, and volume distributions. 

TABLE 8.4 Average Abundances of Major Elements in Soil and Crustal Rock 

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Shaw, G. E., Transport of Asian Desert Aerosol to the Hawaiian Islands, . /. Appl. Meteorol., 19, 1254-1259 (1980). 

Turpin, B. J., P. Saxena, G. Allen, P. Koutrakis, P. McMurry, and L. Hildeniann, Characterization of the Southwestern Desert Aerosol, Meadview, AZ, ./. Air Waste Manage. Assoc., 47, 344-356... 

In case of the pollution import by cool tropical air flows (BT If), die distribution of aerosol surface area versus particle size in the cloud generallly follows curves 3 and 4, but the dominating mode of the size spectrum occurs at the radius of i=0.15 pm. The cloud composition is likely enriched with a saline component of a desert aerosol (r<0.4 pm) and by... 

Desert aerosol 3600 m Elevation Marine air masses Marine air masses advected by strong winds from the Atlantic Ocean Urban pollution, inversion layer... 

Rahn KA, Borys RD, Shaw GE, Schiitz L and Jaenicke R (1979) Long range impact of desert aerosol and atmospheric chemistry two examples. In Saharan Dust. SCOPE 14, Wdey, New York. 

Desert aerosol, of course present over deserts, actually extends considerably over adjacent regions such as oceans (Jaenicke and Schutz 1978 d Almeida and Schutz 1983 Li et al. 1996). The shape of its size distribution is similar to that of remote continental aerosol but depends strongly on the wind velocity. Its number distribution tends to exhibit three overlapping modes at diameters of 0.01 pm or less, 0.05 pm, and 10 pm, respectively (Jaenicke 1993) (Figure 8.22). An average composition of soils and crustal material is shown in Table 8.4. The soil composition is similar to that of the crustal rock, with the exception of the soluble elements such as Ca, Mg, and Na, which have lower relative concentrations in the soil. 

Particulate matters are classified in different types, depending on their origins. While marine aerosols are formed of sea salt particles, remote continental aerosols are of primary particles (Uke dust, pollens and plant waxes), as well as secondary oxidation products. Moreover, desert aerosols, which resemble remote continental aerosols in their shape and size, are found over deserts and adjacent regions and strongly depend on the wind velocity. Urban aerosols are then considered a... 

Desert aerosols exhibit some of the highest concentrations of coarse particles of any of the atmospheric aerosols and can be wind-transported virtually anywhere around the world. Desert particles can contain essential minerals and can play a significant role in fertilizing agricultural regions that lie great distances away from the deserts from which the particles originated [117]. 

Both H2SO4 and HF catalysts suffer from substantial drawbacks. Anhydrous HF is a corrosive and highly toxic liquid with a boiling point close to room temperature. Tests in the Nevada desert showed that, if released into the atmosphere, HF forms stable aerosols, which drift downwind at ground level for several kilometers. In 1987, the accidental release of gaseous HF in Texas City resulted in emergency treatment for several hundred people (9). Therefore,... 

In summary, the variance in the measured fine particle scattering coefficient, bgp was dominated by sulfate concentrations. Organics and crustal species were much less important statistically. The inferred mass scattering effeciency for sulfates was intermediate between other desert values and Los Angeles. The statistical results for China Lake are quite similar to those by other investigators at other locations, even though only the fine aerosol was sampled at China Lake. 

Gatz, D. F., and J. M. Prospero, A Large Silicon-Aluminum Aerosol Plume in Central Illinois North African Desert Dust Atmos. Em iron., 30, 3789-3799 (1996). 

Smyth HDC, Garmise RJ, Cooney DJ, Zimmerer RO, Pipkin JD, Hickey AJ. Influence of physical form of Captisol particles on performance as a dry powder aerosol carrier. Paper presented at Respiratory Drug Delivery IX, Palm Desert, California, 2004. 

Global aerosol levels as measured by the Earth Probe, ADEOS, tfra/Nimbus-7 satellites can befound at this web address. Scientists use this data to observe a wide range of phenomena, such as desert dust storms, forest fires, and biomass burning. 

As part of some international and national projects, many measurements of atmospheric optical thickness were carried out. By using passive satellite sensors, estimates can be averaged vertically over a surface pixel. Therefore, to get a deeper understanding of the optical thickness of atmospheric layers, aircraft measurements are made which give the vertical distributions both of tropospheric aerosols and other characteristics of the atmosphere. Among successful airborne experiments we should highlight the ITOP, SHADE, and SAMUM experiments. These experiments made it possible to study the transformation of aerosols during the distant transport of smoke and desert dust. 

Millard, G.C., Fraley, L. Markham, O.D. (1983) Deposition and retention of141 Ce and 134Cs aerosols on cool desert vegetation. Health Physics, 44, 349-57. 

Figure 7.2 Solid-state speciation in a crustal aerosol collected close to the Saharan Desert and an urban aerosol collected in the UK (Spokes et al., 1994). Results are expressed as a percentage of the total elemental concentration and obtained using a three stage sequential leach using the method of Chester et al. (1989). Stage one uses 1.0 M ammonium acetate to release loosely bound metals. Stage two involves addition of 1.0M hydroxylamine hydrochloride in 25% acetic acid to the residue to release metals held within the oxide and carbonate phases. Stage three uses nitric acid and hydrofluoric acid to break down the aluminosilicate lattice and release metals associated with the crustal fraction of the aerosol.

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